Dealumination of HBEA zeolite by steaming and acid leaching: distribution of the various aluminic species and identification of the hydroxyl groups

A series of HBEA samples were prepared by dealumination through steaming or treatment by hydrochloric acid of a parent commercial zeolite. Treatments with acid solutions were shown to cause a rapid dissolution of the extraframework Al (EFAL) species, especially the monomeric ones and a slow dissolution of the framework Al (FAL) atoms of bridging OH groups and structure defects. Steaming at high temperatures (500-700 degrees C) causes both an extraction of FAL atoms and a significant increase in the degree of polymerization of the EFAL species. A quantitative distribution of the various Al species of the parent HBEA zeolite was established. The nature of the hydroxylated Al species responsible for the IR bands in the OH region was specified: the band at 3607 cm(-1) was ascribed to bridging OH groups responsible for the Bronsted acidity, that at 3660 cm(-1) to monomeric and polymeric EFAL species, that at 3680 cm(-1) to hydroxylated EFAL clusters resulting from acid extraction of Lewis framework defects; that at 3780 cm(-1) to both monomeric EFAL species and framework defects with Lewis acidity. (c) 2005 Academie des sciences. Published by Elsevier SAS. All rights reserved.